Components for electronics and for low-voltage technology are sensitive to external influences and are corrodible. To guarantee their operation, these components must be protected from unfavorable environmental influences such as moisture, aggressive chemicals and dust as well as from mechanical damage. Nowadays this takes place in technology primarily by protectively covering or embedding the components with curable, i.e. thermoplastic molding compounds, also called molding materials. By far, epoxide resin molding compounds have become the leading family of this application field due to their good processing behavior and the good properties of the molded materials and a favorable price/efficiency ratio. An overview of the composition, processing and material properties and use of epoxide resin molding compounds is found e.g. in G. W. Becker and D. Braun, "Kunststoffhandbuch" (Plastics Handbook), Carl Hasset Verlag Munich, Vienna 1988, Vol. 10 "Duroplaste" (Thermoserring Plastics), pp. 338 to 367.
Epoxide resin molding compositions are with inorganic filler materials highly-filled mixtures of epoxide resins with curing agents, accelerators, flameproofing agents, lubricating and release agents, pigments and other additives such as flexibilizers and coupling reagents. They are produced either in the dry mixing process, melting process, or impregnation process and are distributed commercially as virtually dust-free, granular material or in the form of pellets. A prereaction of the resinous mixture takes place during production and dressing preparation. For the handling and further processing of the molding compositions, it is important that, on the one hand, the pre-reacted mixture be very stable at low temperatures, that is, e.g., be storable below 5.degree. C. for 6 months, and, on the other hand, melt quickly at the processing temperature (approx. 150.degree. to 180.degree. C.), become well able to flow and cure quickly with the least possible reactive shrinkage. Cycle times of a few minutes are being currently realized during the encasement of electronic components right up to their being released from the mold. However, one is still striving to reduce this time further.
The requirement for a highest possible glass transition temperature T.sub.G is acknowledged for both the processing as well as for the protective function of the cured molding compositions. This temperature T.sub.G should lie at least above the mold temperature of 150.degree. to 180.degree. C. in order to guarantee a sufficient mold-release rigidity during the molding process. The glass transition temperature should be higher than the highest locally-appearing operating and processing temperatures for the optimum protection of the components because otherwise important properties of the molded material will deteriorate rapidly when the glass transition temperature is exceeded. Thus, for instance, the diffusion rate of moisture and other materials sharply increases; the dielectric constant and the dissipation factor increase and, due to the elevation of the thermal expansion coefficient the transverse strain between the molding compositions and the component increases and can possibly cause damage to the component. Since a high temperature strain arises during the soldering process (soldering bath temperature: 270.degree. to 290.degree. C., the T.sub.G should be &gt;200.degree. C.
The sensitivity of microelectronic components to mechanical wear and tear increases with their increasing miniaturization so that the stresses exerted on the components during temperature changes are no longer tolerable in conventional protective covering compositions. Recently, therefore, so-called "low-stress" molding compounds have been developed which only exert slight force on the components when the temperature changes. This "low stress" behavior property is obtained through molding compound additives such as organopolysiloxanes or functional butadiene/acrylnitrile polymers, which retain their flexibilizing effect at lower temperatures (c.f.: US Pat. No. 4,701,482, JP-OS 62-214650, JP-OS 62-128162).
To maintain the protective function of the molding compositions, it is important that the molding compositions: be as free as possible from corrosive constituents such as C1.sup.-, Br.sup.-, and Na.sup.+, hydrolyzable chlorine and alpha-radiating impurities; have a good substrate adhesion after curing; be resistant to moisture and organic solvents; and be impermeable and satisfy the mechanical and thermal property requirements (bending strength .gtoreq.100 N/mm.sup.2, impact resistance .gtoreq.5 Nmm/mm.sup.2, linear expansion coefficient .alpha..about.15 to 25.times.10.sup.6 K.sup.-1).
Furthermore, the cured molding compositions must be inflammable or self-extinguishing and withstand one of the most demanding standard material tests, namely the flammability test according to UL 94V, with a V-O rating. During this test, five vertically-clamped standard test pieces, respectively, are twice held in flames on the lower end for 10 seconds each. The sum of the ten postburning times, which cease at extinguishment, must be &lt;50 seconds and no single value may exceed 10 seconds. This requirement is difficult to fulfill, above all at thin wall thicknesses of 1.6 nun and under, as is typical in the electronics industry.
Epoxide resin molding compositions found in technical application fulfill these requirements only because they contain up to 80% inflammable inorganic filler materials and the remaining portion of reactive resin is fortified to be virtually inflammable by considerable portions of core-brominated aromatic constituents or additives and high concentrations of antimony trioxide. The problems with these compositions consist in that they are, on the one hand, indeed excellent, effective flameproofing agents; on the other hand, however, they also have some very dangerous properties. Antimony trioxide is on the list of carcinogenic chemicals. Aromatic bromine compounds not only split off bromine radicals and hydrobromic acid during thermal decomposition which cause pronounced corrosion. In addition, during decomposition in the presence of oxygen, the highly brominated aromatics in particular can form highly toxic polybromodibenzofurans and Polybromodibenzodioxins. Moreover, the disposal of bromine-containing waste materials and toxic waste presents considerable difficulties.
The epoxide resin molding compositions found in technical application do indeed have a very favorable processing behavior property, but after curing they only reach a glass transition temperature in the range of 150.degree. to 180.degree. C. Materials which fulfill the requirement for elevated heat resistance are molding compositions on a polyimide base. However, due to the considerably higher material costs and their poor processing behavior property, which requires higher curing temperatures and longer curing times, the technical application of such molding compositions remains limited to special applications. As a possible alternative to the epoxide resins found in technical application, combinations of maleinimides with alkenylphenols and/or alkenylphenol ethers (DE-OS 26 27 045), of maleinimides, polyallylphenols and epoxide resins (JP-OS 53-134099) or combinations of alkenylaryloxy-group-containing s-triazine compositions and polymaleinimides (EP-OS 0 263 915) are discussed.
A comparatively cost-effective resin system is obtained when aromatic and/or heterocyclic polyepoxide resins, i.e. polyglycidyl compounds, are combined with aromatic polyamines as a curing agent. These kinds of polyamines, which e.g. are known from DE-PS 27 43 680, produce particularly age-stable, heat-deformation resistant lattice network polymers. It can be seen from EP-OS 0 271 772 that while using 1.3.5-tris(3-amino-4-alkylphenyl)-2.4-6-trioxo-hexahydrotriazines as a curing agent, molded compositions are obtained which have glass transition temperatures to 245.degree. C. and are distinguished by favorable processing and working properties.
The disadvantage of not being sufficiently inflammable is acknowledged for all of the resin systems mentioned. Therefore, to fulfill the requirement--which is indispensable for electronics--of withstanding the flammability test according to UL 94V with a rating V-O, the use of highly effective bromine-containing flameproofing agents and antimony trioxide cannot be dispensed with (c.f. DE-OS 27 00 363). This has the consequence that one must allow for, on the one hand, the potential for danger connected with bromine compounds and antimony trioxide and, on the other hand, a deterioration of the quality of the thermo-mechanical properties effected by the bromine compounds. Namely, it is known that the addition of core-brominated aromatics causes a reduction of the glass transition temperature. Thus, it was found, e.g., that the glass transition temperature of polyimides is reduced by the addition of bromine compounds by 40.degree. to 70.degree. C. (c.f. "Polymer Journal", Vol. 20 (1988), pp. 125 fol.). In the systems of epoxides and polyamines described in EP-OS 0 271 772, a reduction of the T.sub.G by approximately 50.degree. C. to values below 200.degree. C. is found during a partial substitution of the epoxide constituents by the corresponding brominated compound according to a total bromine concentration of 4%.
For these reasons there has not been a lack of attempts to replace the bromine-containing flameproofing agent in reaction resin systems with less problematical substances. Thus, for example, filler materials were suggested which have a quenching gas effect such as hydrated aluminum oxides (c.f. "J. Fire and Flammability", Vol.3 (1972), pp. 51 fol.), alkaline aluminum carbonates (c f "Plast Engng" Vol 32 (1976), pp 41 fol.) and magnesium hydroxides (EP-OS 0 243 201) as well as vitrifying filler materials such as borates (c.f. "Modern Plastics" Vol 47 (1970), pp. 140 fol.) and phosphates (U.S. Pat. Nos. 2,766,139 and 3,398,019). However, associated with all of these filler materials is the disadvantage that, in part, they considerably deteriorate the mechanical, chemical and electrical properties of the molded materials.
The flame-retarding effectiveness of red phosphorous has also already been described (GB-patent 1 112 139), optionally in combination with finely dispersed silicon dioxide or hydrated aluminumoxide (U.S. Pat. No. 3,373,135). In this manner, molded materials are obtained which limit the application for electrotechnical and electronic purposes due to phosphoric acid which may possibly result under unfavorable conditions and the corrosion which is connected with the phosphoric acid. Furthermore, organic phosphorous compounds such as phosphoric acid esters, phosphonic acid esters and phosphines have already been suggested as flame-retarding additives (c.f. W. C. Kuryla and A. J. Papa "Flame Retardancy of Polymeric Materials", Vol. 1, pp. 24-38 and 52-61, Marcel Dekker Inc., New York, 1973). Since these compounds are known for their "plasticizing" properties and are used globally to a large extent as plasticizers for polymers (GB-patent 10 794), this alternative, too, is not very promising with regard to the required thermal resistance of molded materials.
A more effective possibility for regulating the inflammability of epoxide resins consists in using phosphorous compounds which can be anchored in the polymer network such as epoxide-group-containing phosphorous compounds. The thermo-mechanical properties of the molded materials obtained in this case during curing, however, are not sufficient. Thus, for example, molded materials with a T.sub.G of 45.degree. to 80.degree. C. are obtained during the aminic curing of epoxide resins resulting from methyl diglycidyl phosphonate and dicarboxylic acids (c.f. "Vysokomol. Soedin.", Ser. B. 29 (1), pp. 45 to 47 (1987)). This agrees with the experience that phosphoric acid ester groupings, both in the main polymer chain as well as in the side chain, basically cause a plasticization and thus a lowering of the glass transition temperature (c.f. "Journal of Macromolecular Science", Vol. Cl, No. 1 (1967), pp. 3 fol.). Moreover, to a large extent these compounds are liquid or crystalline and therefore do not come into question for regulating the inflammability of epoxide resins since they either greatly lower the softening point of the solid resins, produce stickiness or--in the case of crystalline compounds recrystallize (c.f. DE-OS 25 38 675). In all known publications, epoxide-group-containing phosphorous compounds are therefore converted first in a prereaction with bisphenols or phenolic resins (DE-OS 25 38 675 and JP-OS 58-185631), with dicarboxylic acids (c.f. Vysokomol. Sosdin."Ser. B. 29 (1), pp. 45-47 (1987)) or with polyester resins from dihydroxy compounds and dicarboxylic acids (JP-OS 50-043221) and only then are the converted compounds cured --primarily ionically-- in a mixture with the epoxide resins. However, the inflammability achieved in this manner is modest. Thus, limiting oxygen index values ("LOI values") of 23.5 to 24, i.e. values like those one finds in flammable materials such as wool (LOI =25), are achieved in resins which are obtained by means of a prereaction with bisphenols (c.f. DE-OS 25 38 675), whereas the LOI values for known inflammable materials such as polysulphone (LOI =30), polyvinyl chloride (LOI =42), polyvinylidene chloride (LOI =60) and polytetrafluoroethylene (LOI =95) lie considerably higher (c.f. D. W. v. Krevelen "Properties of Polymers", Elsevier Scientific Publishing Comp., Pasterdam, Oxford, N.Y., 1976, pp. 526 fol.). In the case of the conversion products of polyester resins with triglycidyl phosphates (c.f. JP-OS 50-043221), even halogen compounds and antimony trioxide must be added to regulate the inflammability of polyester fibers.
It is therefore an object of the invention to specify epoxide resin molding compositions which are accessible in a cost-effective manner and are comparable in processibility to epoxide resin molding compounds found in technical application, and which yield inflammable molded materials which can be rated as V-O according to UL 94 V with a highest possible glass transition temperature (T.sub.G &gt;200.degree. C.) and a lowest possible thermal expansion coefficient (.about.15 to 25.times.10.sup.6 K.sup.-1) without the addition of halogen compounds or antimony trioxide.